1. Field of the Invention
The present invention relates to a focal length switching camera capable of performing focal length switching even during photometric operation.
The present invention further relates to an electrically-operated focal length switching type camera in which a lens unit may be encased within a camera body even if a battery voltage is less than a normal value.
2. Description of the Prior Art
In the past, a lens exchange type camera in which a standard lens can be exchanged with a telephotolens having along focal length when a remote object is photographed in a large size, has been widely used. However, in this kind of camera, it is cumbersome to carry an exchange lens or replace a lens, and therefore, a camera in which two kinds of focal lengths may be switched by simple operation has been recently developed.
The two-focus camera of this kind encases therein two optical systems different in focal length from each other and in photographing, either optical system is selected by manual operation. The switching operation of the optical system becomes simpler as compared with prior art camera which involves cumbersome of lens exchange but this exchange requires a certain degree of time and therefore when a moving object is photographed, one might miss a shuttering chance, and it is difficult to switch the focal length while performing framing.
In view of the foregoing, the present inventors have proposed a two-focus camera in which a motor is started by operation of a button to move a lens unit thereby automatically switching the focal length.
In the focal length switching type camera of this kind, the focal length is sometimes switched while performing framing, and when a lens optical system is different, the brightness of the lens is different and therefore when it is switched to the long focal point side, a short in brightness sometimes results. It is therefore preferable that the focal length may be switched while performing photometric operation.
On the other hand, in recently available cameras, not only winding and unwinding of a film but even shutter driving and movement of a lens for focus adjustment are electrically or electromagnetically accomplished, and because of this, a consuming degree of a power source is extremely great. In the camera of this kind, when a voltage of the battery drops, the aforementioned various functions cannot be assured. Therefore, for assuring the performance of the camera, a battery voltage is checked and when the voltage lowers than the value of assuring the performance of the camera, a user is cautioned to urge replacement of a battery.
Incidentally, in a camera of the type in which the focal length is switched by moving an auxiliary lens unit into and out of a camera body, which is one type of the aforementioned two-focus camera, when the battery voltage lowers than the performance assurance value, i.e., the normal value, during the use of the camera in the state where the main lens unit is projected from the camera body (normal telephotographing), the lens unit driving mechanism becomes inoperative and the camera unit cannot be withdrawn into the camera body, and as the result the camera cannot be sometimes received into the case, which is inconvenient in handling.